Field of the Invention
According to the invention there is provided a method of providing heat to promote an endothermic reaction or be extracted as sensible heat, the method comprising providing first passage means having first inlet means thereto and first outlet means therefrom, when considering fluid flow along said first passage means towards the first outlet means from the first inlet means said first passage means having an upstream portion leading towards a downstream portion of said passage means, second passage means having second inlet means thereto and second outlet means therefrom, third passage means having third inlet means thereto and third outlet means therefrom, heat conducting wall means provided between said upstream portion of the first passage means and the second passage means and between said downstream portion of the first passage means and the third passage means, introducing combustible gas and oxidant into the upstream portion of the first passage means wherein said fuel gas and oxidant are heated by heat conducted through said wall means from the second passage means, burning the combustible gas with said oxidant in said downstream portion of the first passage means, supplying the resultant products of combustion to the second inlet means to the second passage means for said products of combustion to flow along the second passage means to said second outlet means wherein the products of combustion give up heat which is conducted through said wall means to said upstream portion of the first passage means to heat further introduced said combustible gas and oxidant, and either (i) introducing one or more fluid substances into the third passage means through the third inlet means to undergo an endothermic chemical reaction using heat conducted through said wall means from said downstream portion of the first passage means such that products of the reaction leave through said third outlet means or (ii) introducing an heatable fluid into the third passage means to receive heat conducted through said wall means from said downstream portion of the first passage means such that the heatable fluid becomes heated and thereafter leaves through the third passage means bearing sensible heat.